Lift trucks are designed in a variety of configurations to perform a variety of tasks. One problem with lift trucks is that they can oscillate or vibrate about any of the X-axis, Y-axis and Z-axis (see FIG. 1). For example, when an operator stops the truck abruptly or abruptly changes direction, or both, vibrating motion about any of the X-axis, Y-axis and Z-axis can be felt by the lift truck operator. The vibrations can be more noticeable when the lift truck's mast is vertically extended. While such vibrating motion will not tip the truck, the motion can be disconcerting to the operator. Normally an operator will slow down and allow the vibrating motion to naturally dissipate before resuming travel. These unwanted vibrations can reduce the efficiency of the operator and the overall productivity of lift truck operations.
Today's lift trucks are often performance limited in an effort to maintain acceptable dynamic behavior. These performance limitations are passive and are normally universally applied independent of the current operating condition. An example would be an algorithm to limit vehicle speed according to the elevated height. The algorithm, however, may not consider the load on the forks and therefore may be returning a sub-optimal travel speed for the lift truck, which may be quite limiting to the operator's productivity. Labor cost can be the largest component of operating costs for a lift truck.
One method for improving lift truck performance includes performing a static center-of-gravity (CG) analysis while the lift truck is at rest and limiting lift truck operating parameters accordingly (for example, maximum speed and steering angle). However, this static calibration does not dynamically account for lift truck motion, changing lift heights, or environmental factors such as the grade of a driving surface, for example.
Other methods for improving vehicle stability common in consumer automobiles include calculating vehicle CG during vehicle movement and employing an anti-lock braking system (ABS) to modify the cornering ability of the vehicle. These prior methods only consider two-dimensional vehicle movement (forward-reverse and turning) and do not account for three-dimensional CG changes of a lift truck due to load weights being lifted and lowered while the lift truck is in motion. In addition, these methods do not account for maintaining a lift truck within defined bounds and keeping the lift truck from deviating from its intended path.
If the vibrating motion of the lift truck can be mitigated or even cancelled, the lift truck would then be capable of traveling faster, providing a more comfortable ride for the operator and improving productivity.
What is needed is a lift truck configured to dynamically optimize lift truck performance by maintaining the lift truck within defined bounds and keeping the lift truck from generally deviating from its intended path.